In Javascript if you try to run this code then only #4 statement will print the value.
<script type="text/javascript">
function print(obj){
console.log(obj);
}
if(undefined){
print ("undefined");
}
if(null){
print('null');
}
if(isNaN(null)){
print('isNaN(null)');
}
if(isNaN(undefined)){ // only this statement will come true
print('isNaN(undefined)');
}
</script>